[Chaste]

Hi all,

This is based on Refractive index detector.

in the above picture, there is a small negative peak beside the main product peak. Can anyone explain to me what such a peak may indicate?

[Chaste]

Edit: I made a mistake. The small little peak is actually my analyte, as I reversed the polarity on my machine. However, the intense peak is something that is an anomaly any suggestions on what it could be?

[Arkcon]

That large unknown peak could be anything -- the injection disturbance, or your sample's dilution solvent, or another component chromatographing out.  Refractive index detectors are weird, when you compare them to UV detectors, their response can be huge or tiny compared to actual amount coming through (you probably knew that, I'm just trying to help out other people who might not know)  A bit more about your sample, matrix, and eluent would help get a better answer for you.

*[EDIT]*

Correct mis-spelling

[Chaste]

I am using a water/MeOH 70:30 eluent. Sample, if I remember correctly, it should be Ethanol. I'm analysing pure compounds.

[Arkcon]

Well, it still might be some impurity leaching through.  You can try to narrow down the identity with some blank runs (to detect column leaching), or mobile phase injections (to detect injector effects) or sample diluent injections to see if your sample has a new impurity or not.